Acute and chronic copper toxicity to a saltwater cladoceran Moina monogolica Daday

The objective of this study was to evaluate the sensitivity of a saltwater cladoceran Moina monogolica Daday to copper toxicity. Acute and chronic toxicity tests were conducted according to the American Society for Testing and Materials (ASTM) guidelines. The 24- and 48-h LC(50)s and their 95% confidence intervals (CIs) were calculated as 154.21 (135.50-182.05) microg Cu/L and 106.07 (99.77- 112.36) microg Cu/L , respectively, based on measured copper concentrations. When compared with different phyla or classes of estuarine organisms, M. monogolica had moderate sensitivity and was suitable to be used as an indicator organism in the Changjiang estuary. Eight end points of longevity, number of broods, brood size, total reproduction, time to first brood, intrinsic rate of natural increase (r(m)), net reproductive rate (R(0)), and mean generation time (T) used to evaluate chronic effects were affected at chronic copper concentrations. Comparisons of chronic effects showed that toxicity mechanisms of dissolved copper are different from those of dietary exposure. The EC(20)s, EC(50)s, and their 95% CIs of end points were calculated using linear regression equations. The geometric mean generated the maximum-acceptable-toxicant concentration of 6.74 microg Cu/L between the no-observed-effect concentration of 5.06 and the lowest-observed-effect concentration of 8.99 microg Cu/L for brood size, total reproduction, r(m), and R(0), and 12.1 microg Cu/L between 8.99 and 16.29 microg Cu/L for longevity and number of broods as the end points, respectively. The EC(20) of R(0) appeared to be the most sensitive at 3.82 microg Cu/L among the end points. Results showed that aquatic organisms were possibly negatively affected at sites of higher copper concentrations in the Changjiang estuary. Further research is needed to evaluate the direct or indirect effects of copper more comprehensively to protect aquatic organisms and their habitats in the Changjiang estuary.